Implantable neuromodulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations, Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Furthermore, Functional Electrical Stimulation (FES) systems, such as the Freehand system by NeuroControl (Cleveland, Ohio), have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
These implantable neuromodulation systems typically include one or more electrode carrying modulation leads, which are implanted at the desired stimulation site, and a neuromodulator (e.g., an implantable pulse generator (IPG)) implanted remotely from the stimulation site, but coupled either directly to the neuromodulation lead(s) or indirectly to the neuromodulation lead(s) via a lead extension. The neuromodulation system may further comprise a handheld patient programmer to remotely instruct the neuromodulator to generate electrical stimulation pulses in accordance with selected stimulation parameters. The handheld programmer in the form of a remote control (RC) may, itself, be programmed by a clinician, for example, by using a clinician's programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon.
Electrical modulation energy may be delivered from the neuromodulator to the electrodes in the form of a pulsed electrical waveform. Thus, modulation energy may be controllably delivered to the electrodes to modulate neural tissue. The combination of electrodes used to deliver electrical pulses to the targeted tissue constitutes an electrode combination, with the electrodes capable of being selectively programmed to act as anodes (positive), cathodes (negative), or left off (zero). In other words, an electrode combination represents the polarity being positive, negative, or zero. Other parameters that may be controlled or varied include the amplitude, duration, and rate of the electrical pulses provided through the electrode array. Each electrode combination, along with the electrical pulse parameters, can be referred to as a “neuromodulation parameter set.”
Of course, neuromodulators are active devices requiring energy for operation, and thus, the neurostimulation system may oftentimes includes an external charger to recharge a neuromodulator, so that a surgical procedure to replace a power depleted neuromodulator can be avoided. To wirelessly convey energy between the external charger and the implanted neuromodulator, the charger typically includes an alternating current (AC) charging coil that supplies energy to a similar charging coil located in or on the neurostimulation device. The energy received by the charging coil located on the neuromodulator can then be used to directly power the electronic componentry contained within the neuromodulator, or can be stored in a rechargeable battery within the neuromodulator, which can then be used to power the electronic componentry on-demand.
In the context of an SCS procedure, one or more leads are introduced through the patient's back into the epidural space, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array. After proper placement of the leads at the target area of the spinal cord, the leads are anchored in place at an exit site to prevent movement of the leads. To facilitate the location of the neuromodulator away from the exit point of the leads, lead extensions are sometimes used. The leads, or the lead extensions, are then connected to the IPG, which can then be operated to generate electrical pulses that are delivered, through the electrodes, to the targeted spinal cord tissue. The modulation, and in the conventional case, the stimulation, creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. The efficacy of SCS is related to the ability to modulate the spinal cord tissue corresponding to evoked paresthesia in the region of the body where the patient experiences pain. Thus, the working clinical paradigm is that achievement of an effective result from SCS depends on the neuromodulation lead or leads being placed in a location (both longitudinal and lateral) relative to the spinal tissue such that the electrical modulation will induce paresthesia located in approximately the same place in the patient's body as the pain (i.e., the target of treatment).
Conventional neuromodulation therapies employ electrical stimulation pulse trains at low- to mid-frequencies (e.g., less than 1500 Hz) to efficiently induce desired firing rate of action potentials from electrical pulses (e.g., one pulse can induce a burst of action potentials, or multiple pulses may be temporally integrated to induce on action potential). Such stimulation pulse trains are usually tonic (i.e., the pulse amplitude, pulse rate, and pulse width are fixed). However, neuron response is a dynamic time course that can vary with the sequential stimulation, thereby limiting the volume of neural tissue that may be consistently stimulated. Furthermore, it is known that neural tissue may accommodate, adapt, and/or habituate to a continuous tonic input, resulting in a diminished neural response over time.
Recently, high frequency modulation (e.g., 1.5 KHz-50 KHz), which has been increasingly attractive in neuromodulation for pain management, is employed to block naturally occurring action potentials within neural fibers or otherwise disrupt the action potentials within the neural fibers. Although the underlying mechanisms of high frequency modulation for pain reduction are yet unclear, it has been hypothesized that there are many mechanisms that potentially play a role in reducing pain, including the depletion of neurotransmitter during the sustained modulation, desynchronized firing of multiple neurons, and generation of stochastic noise in neuronal signal transmission or lesioning of pain information. One disadvantage of high-frequency pulsed electrical energy is that it consumes an excessive amount of energy, thereby requiring the neuromodulator device to be charged more often.
Furthermore, although certain conventional stimulation parameters (e.g., pulse amplitude, pulse frequency, and pulse width) of the pulsed electrical energy, whether delivered at a low-, mid-, or high-frequency, can be varied to optimize the therapy, it may be desirable to allow the user to vary other characteristics of the pulsed electrical energy in order to further tailor the pulsed electrical energy to the volume of neural tissue to be modulated.
There, thus, remains an improved technique for delivering pulsed electrical energy to a patient.